|  | 1.5 | Routing and the Different Classes of Routing Protocols
| 1.5.10 | Link-state routing
The second basic protocol used for routing is the link-state protocol. Link-state routing protocols maintain a complex database of topology information. Whereas the distance-vector protocol has nonspecific information about distant networks and no knowledge of distant routers, a link-state routing protocol maintains full knowledge of distant routers and how they interconnect. Link-state routing uses link-state advertisements (LSAs), a topological database, the SPF protocol, the resulting SPF tree, and finally, a routing table of paths and ports to each network. Engineers have implemented this link-state concept in OSPF routing.